Field of the Invention
The present invention relates to a sheet binding processing apparatus, an image forming system, and a sheet binding processing method and, more particularly, to, for example, a method of stacking sheets that have undergone binding processing.
Background Art
There is a case in which a sheet processing apparatus for performing various types of post-processing on a sheet-like printing medium on which an image has been formed by an image forming apparatus is provided in a conventional image forming system. As such a sheet processing apparatus, there is known, for example, a sheet binding processing apparatus (to be referred to as a needle stapler hereinafter) with a stapler that binds a bundle made of a plurality of printing media by using binding members such as metal staples. Binding processing by the needle stapler will be referred to as needle stapling processing hereinafter.
The sheet binding processing apparatus performs the above-described sheet binding processing and discharges/stacks printing media to/on a predetermined tray. It is necessary to set the height of the printing media stacked on that tray to a height that does not inhibit discharge of the printing media. For this reason, an operation is suspended when the number of printing media stacked on that tray reaches a predetermined number. In such a sheet binding processing apparatus, a bundle of printing media that has undergone needle stapling processing becomes higher by portions of staples. If such a bundle is stacked on the tray, a sheet height cannot be determined correctly, the bundle may block a printing medium discharge port, and discharge of the printing media may be left undone. Moreover, the bundle unpiles as the portions of the staples become thicker, making it impossible to align and stack the bundle.
In order to solve such problems, patent literature 1 proposes control capable of suspending an operation not only by the number of sheets but also by the number of stapled bundles. Patent literature 2 proposes an arrangement in which the number of sheets discharged to and stacked on a tray is converted into a stacking point and counted, the stacking point is counted in correspondence with a paper size or a non-binding mode/binding mode, and the total is controlled so as not to exceed the predetermined value of the tray.